Immersion microscope objective and microscope using the same

ABSTRACT

An immersion microscope objective includes, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, wherein the first lens group includes a first lens surface and a second lens surface, the first lens surface is positioned nearest to the object side and the second lens surface is positioned on an image side of the first lens surface and nearest to the first lens surface, and the following conditional expression (1) is satisfied: 
       −3≦( r   G12   /f )×( NA   ob   /nd   imm ) 2 −1.7  (1)
         where   r G12  denotes a radius of curvature at the second lens surface,   f denotes a focal length of an entire system of the immersion microscope objective,   NA ob  denotes an object-side numerical aperture of the immersion microscope objective, and   nd imm  denotes a refractive index of an immersion liquid for a d-line.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2013-244336 filed on Nov.26, 2013; the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an immersion microscope objective, anda microscope using the same.

2. Description of the Related Art

Recently, in research in biology and genetics, there is a desire anddemand to perform fluorescence observation on a thick and livebiological specimen with high resolving power. To meet this demand, amicroscope objective is required to have a large numerical aperture(high NA) and high magnification.

The microscope objective of this kind is often used in a confocal laserscanning microscope. A confocal laser scanning microscope has a verysmall depth of focus, so it can obtain a sectioning image of a specimen.In order to obtain an accurate sectioning image, the microscopeobjective is required to have high flatness of a field.

An immersion microscope objective is the microscope objective that cansatisfy such requirements. In an immersion microscope objective, thereis an immersion liquid between the immersion microscope objective and aspecimen. Thus, when the immersion microscope objective is used toobserve a deep portion of a biological specimen, spherical aberrationmay occur, depending on the type of the immersion liquid used, becauseof the difference between the refractive index (1.33 to 1.45) of thebiological specimen and the refractive index of the immersion liquid. Inorder to reduce such spherical aberration, it is desirable that thebiological specimen and the immersion liquid have similar refractiveindices.

Specifically, as an immersion liquid, the following are desirable: water(refractive index: 1.33), culture solution (refractive index: 1.33),silicone oil (refractive index: 1.40), and a mixture of glycerin andwater (refractive index: 1.33 to 1.47). Further, it is preferable thatan immersion microscope objective also has its aberrations favorablycorrected for these immersion liquids.

Furthermore, the spherical aberration varies depending on the positionbeing observed (i.e. the depth from the surface of the biologicalspecimen). Therefore, it is desirable that the immersion microscopeobjective is provided with a correction collar, which enables correctionof the spherical aberration.

As an immersion microscope objective having a large numerical aperture,an immersion microscope objective disclosed in Japanese PatentApplication Laid-Open No. 2008-170969 is available. In the immersionmicroscope objective disclosed in Japanese Patent Application Laid-OpenNo. 2008-170969, the magnification and numerical aperture are 60× and1.4, respectively, in the case of an oil immersion microscope objective,and 60× and 1.3, respectively, in the case of a silicone immersionmicroscope objective.

SUMMARY OF THE INVENTION

An immersion microscope objective according to the present inventioncomprising, in order from an object side:

a first lens group having a positive refractive power; a second lensgroup having a positive refractive power; and a third lens group havinga negative refractive power; wherein

the first lens group includes a first lens surface and a second lenssurface,

the first lens surface is positioned nearest to the object side, and thesecond lens surface is positioned on an image side of the first lenssurface and nearest to the first lens surface, and

the following conditional expression (1) is satisfied:

−3≦(r _(G12) /f)×(NA _(ob) /nd _(imm))²≦−1.7  (1)

where

r_(G12) denotes a radius of curvature at the second lens surface,

f denotes a focal length of an entire system of the immersion microscopeobjective,

NA_(ob) denotes an object-side numerical aperture of the immersionmicroscope objective, and

nd_(imm) denotes a refractive index of an immersion liquid for a d-line.

A microscope according to the present invention comprising:

a light source; an illumination optical system; a main-body section; anobservation optical system; and a microscope objective, wherein

the immersion microscope objective described above is used for themicroscope objective.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view along an optical axis, showing anoptical arrangement of an immersion microscope objective according to anexample 1 of the present invention;

FIG. 2 is a cross-sectional view along an optical axis, showing anoptical arrangement of an immersion microscope objective according to anexample 2 of the present invention;

FIG. 3 is a cross-sectional view along an optical axis, showing anoptical arrangement of an immersion microscope objective according to anexample 3 of the present invention;

FIGS. 4A, 4B, 4C, and 4D are aberration diagrams of the immersionmicroscope objective according to the example 1;

FIGS. 5A, 5B, 5C, and 5D are aberration diagrams of the immersionmicroscope objective according to the example 2;

FIGS. 6A, 6B, 6C, and 6D are aberration diagrams of the immersionmicroscope objective according to the example 3;

FIG. 7 is a cross-sectional view of a tube lens; and

FIG. 8 is a diagram of a microscope having the immersion microscopeobjective of the present invention used therein.

DETAILED DESCRIPTION OF THE INVENTION

An immersion microscope objective according to an embodiment comprises,in order from an object side: a first lens group having a positiverefractive power; a second lens group having a positive refractivepower; and a third lens group having a negative refractive power;wherein the first lens group includes a first lens surface and a secondlens surface, the first lens surface is positioned nearest to the objectside and the second lens surface is positioned on an image side of thefirst lens surface and nearest to the first lens surface, and thefollowing conditional expression (1) is satisfied:

−3≦(r _(G12) /f)×(NA _(ob) /nd _(imm))²≦−1.7  (1)

where

r_(G12) denotes a radius of curvature at the second lens surface,

f denotes a focal length of an entire system of the immersion microscopeobjective,

NA_(ob) denotes an object-side numerical aperture of the immersionmicroscope objective, and

nd_(imm) denotes a refractive index of an immersion liquid for a d-line.

The immersion microscope objective (hereinafter, referred to as the“objective” as appropriate) according to the present embodiment is animmersion microscope objective which is used together with an immersionliquid whose refractive index for the d-line is nd_(imm). The objectiveaccording to the present embodiment includes, in order from the objectside, the first lens group having a positive refractive power, thesecond lens group having a positive refractive power, and the third lensgroup having a negative refractive power. The object side means a sampleside.

If an object-side numerical aperture (hereinafter, simply referred to asthe “numerical aperture”) of the objective is made large, it is possibleto make light with a larger angle of divergence (diffraction angle)incident on the objective from the sample. As a result, it is possibleto observe a microscopic structure of the sample further minutely. Lightwith a large angle of divergence, however, has a high light-ray heightin the first lens group. When such a light ray is bent sharply in thefirst lens group, high order aberration is liable to occur in the firstlens group.

In the objective according to the present embodiment, the first lensgroup is configured to have a positive refractive power, to therebycause the light ray with a large angle of divergence to be bentgradually through the first lens group. This can suppress the occurrenceof large high order aberration.

Further, the second lens group is also configured to have a positiverefractive power. In the first lens group, as explained above, the lightray with a large angle of divergence is bent gradually. This means thatthe diameter of the light beam exiting the first lens group has notbecome sufficiently small. Therefore, in the second lens group, thelight beam diameter is made to decrease gradually.

The third lens group is configured to have a negative refractive power.In the second lens group, a divergent light beam has been changed to aconvergent light beam. Therefore, in the position of the third lensgroup, the light-ray height is low. Accordingly, with the negativerefractive power of the third lens group, the Petzval's sum can be madesmall. Further, the convergent light beam from the second lens group ischanged to a substantially parallel light beam by the third lens group.

Further, in the objective according to the present embodiment, theconditional expression (1) is satisfied.

When the conditional expression (1) is satisfied, the radius ofcurvature of the second lens surface attains the radius of curvaturethat can suppress the divergence of light ray and the occurrence ofaberration in a well-balanced manner. As a result, it is possible toincrease the object-side numerical aperture, while suppressing theoccurrence of aberration. It should be noted that the second lenssurface is preferably a cemented surface, although it may be either anair-contact surface or a cemented surface.

When falling below the lower limit of the conditional expression (1),the radius of curvature of the second lens surface will becomeexcessively large. In this case, since the angle of incidence of thelight ray incident on the second lens surface will become large, a largespherical aberration will occur. Further, when the second lens surfaceis a cemented surface, a large chromatic aberration will occur.

When exceeding the upper limit of the conditional expression (1), theradius of curvature of the second lens surface will become excessivelysmall. In this case, the negative refractive power at the second lenssurface will become large, and the light-ray height of the axial lightbeam after it has passed through the second lens surface will becomehigh. This leads to occurrence of high order spherical aberration, butit will be difficult to correct such high order spherical aberrationwith the optical system that is located closer to the image side thanthe second lens surface. Further, the radius of curvature will be small,leading to a decreased effective aperture of the second lens surface,making it impossible to increase the object-side numerical aperture.

In the immersion microscope objective according to the presentembodiment, it is preferable that the first lens group converts adivergent light beam to a convergent light beam, the third lens groupincludes an object-side lens component and an image-side lens component,the object-side lens component is disposed nearest to the object sideand the image-side lens component is disposed closer to the image sidethan the object-side lens component, the object-side lens component hasa meniscus shape with a concave surface facing the image side, theimage-side lens component has a meniscus shape with a concave surfacefacing the object side, and that the lens component is a single lens ora cemented lens.

If the divergent light beam cannot be converted to a convergent lightbeam in the first lens group, the height of the light ray passingthrough the second lens group will become high. In such a case, highorder spherical aberration is liable to occur in the second lens group.Thus, in the first lens group, the light ray with a large angle ofdivergence is gradually bent, and also, the divergent light beam isconverted to a convergent light beam. In this manner, the sphericalaberration is favorably corrected in the first lens group, and theoccurrence of high order spherical aberration in the second lens groupis also prevented.

Further, in the third lens group, the object-side lens component isdisposed with its concave surface facing the image side, and theimage-side lens component is disposed with its concave surface facingthe object side. As such, in the third lens group, the two lenscomponents are disposed such that their concave surfaces face eachother, so the third lens group has a so-called Gauss-type lensarrangement. This allows an appropriate negative Petzval's sum to beobtained in the third lens group.

In an objective having a large numerical aperture, a cemented lens isdisposed in a lens group arranged near the object, generally in thefirst lens group. In the cemented lens, two lenses are cemented togetherin the state where the object-side lens is embedded in the image-sidelens. Although it may be possible to obtain a negative Petzval's sum atthe cemented surfaces of the object-side lens (embedded lens) and theimage-side lens, the negative Petzval's sum thus obtained tends to beinsufficient.

Thus, a lens group having a concave surface is disposed closer to theimage side than the first lens group. It is necessary to correct thePetzval's sum by compensating for the insufficient negative Petzval'ssum by that concave surface. In the case where a lens of a meniscusshape is disposed in the lens group having the concave surface, a singlemeniscus-shaped lens alone cannot sufficiently correct the Petzval'ssum. Thus, two meniscus-shaped lenses are used and disposed such thattheir concave surfaces face each other. This configuration can secure asufficient negative Petzval's sum, and accordingly, the Petzval's sumcan be corrected.

Further, with the meniscus-shaped lens disposed such that its concavesurface faces the object side, it is possible to optimally adjust thelight-ray height or angle of the light ray that emerges from theobjective.

It should be noted that the meniscus-shaped lens is preferably acemented lens. This configuration can favorably correct longitudinalchromatic aberration as well as chromatic aberration of magnification.

Further, in the immersion microscope objective according to the presentembodiment, it is preferable that the first lens group includes a firstcemented lens disposed nearest to the object side, the first cementedlens includes an object-side lens and an image-side lens, and thefollowing conditional expression (2) is satisfied:

0.3≦nd _(G1i) −nd _(G1o)≦0.5  (2)

where

nd_(G1i) denotes a refractive index of the image-side lens for thed-line, and

nd_(G1o) denotes a refractive index of the object-side lens for thed-line.

When the conditional expression (2) is satisfied, it is possible to makea divergent light beam with a large angle of divergence incident on theobjective, and it is also possible to convert the incident divergentlight beam with a large angle of divergence to a convergent light beamwith ease.

Here, as the refractive index of the object-side lens and the refractiveindex of the immersion liquid are made close to each other, it ispossible to make a divergent light beam having a large angle ofdivergence incident on the objective, while suppressing the occurrenceof aberration at the boundary between the immersion liquid and theobject-side lens surface. On the other hand, the refractive index of theimage-side lens is appropriately larger than the refractive index of theobject-side lens. Accordingly, the incident divergent light beam with alarge angle of divergence can be bent to approach the optical axis.

When exceeding the upper limit of the conditional expression (2), therefractive index of the image-side lens will become excessively large.In this case, since the sensitivity (rate of change) of sphericalaberration to the lens thickness tolerance will become large, occurrenceof aberration caused by manufacturing errors will become large. Further,in a glass material having a large refractive index, a transmittance ofultraviolet light is low. Therefore, in fluorescence observation usingultraviolet light, it will become difficult to illuminate a sample withsufficiently bright ultraviolet light.

When falling below the lower limit of the conditional expression (2),the refractive index of the image-side lens will become excessivelysmall. In this case, it will be difficult to gradually bend thedivergent light beam with a large angle of divergence, incident on theobjective, such that it approaches the optical axis. Therefore, thelight-ray height of the axial light beam after it has passed through theimage-side lens will become high. This leads to occurrence of high orderspherical aberration, but it will become difficult to correct this highorder spherical aberration with the optical system located closer to theimage side than the image-side lens.

Further, in the immersion microscope objective according to the presentembodiment, it is preferable that the first lens group includes, inorder from the object side, a cemented lens and a single lens, thecemented lens and the single lens each have a positive refractive power,and the following conditional expression (3) is satisfied:

2.2≦f _(G1p) /f≦3.5  (3)

where

f_(G1p) denotes a composite focal length of the cemented lens and thesingle lens, and

f denotes the focal length of the entire system of the immersionmicroscope objective.

When the conditional expression (3) is satisfied, the compositerefractive power of the cemented lens and the single lens can be setappropriately with respect to the refractive power of the overallobjective. This can suppress the divergence of light ray and theoccurrence of aberration in a well-balanced manner. As a result, it ispossible to gradually bend the divergent light beam with a large angleof divergence, incident on the objective, so as to cause it to approachthe optical axis, while suppressing the occurrence of aberration.

When exceeding the upper limit of the conditional expression (3), thecomposite focal length of the cemented lens and the single lens willbecome excessively long. In this case, since the composite refractivepower of the cemented lens and the single lens becomes excessivelysmall, it will become difficult to gradually bend the divergent lightbeam incident on the objective, such that it approaches the opticalaxis. Therefore, the light-ray height of the axial light beam after ithas passed through the single lens will become high. This leads tooccurrence of high order spherical aberration, but it will becomedifficult to correct such high order spherical aberration with theoptical system located closer to the image side than the single lens.

When falling below the lower limit of the conditional expression (3),the composite focal length of the cemented lens and the single lens willbecome excessively short. In this case, since the radii of curvature ofthe lens surfaces of the respective lenses will become excessivelysmall, the spherical aberration will occur. In particular, the radius ofcurvature at the image-side lens surface (air-contact surface) of thecemented lens will become excessively small, so a large sphericalaberration will occur.

Furthermore, since the refractive power of the first lens group willbecome excessively large, positive Petzval's sum will increase. In thiscase, it is preferable that an increase of the positive Petzval's sumcan be cancelled by a negative Petzval's sum in a lens group locatedcloser to the image side than the first lens group, particularly in thethird lens group. However, it will become difficult to secure asufficient negative Petzval's sum in the third lens group.

Further, in the immersion microscope objective according to the presentembodiment, it is preferable that the third lens group satisfies thefollowing conditional expression (4):

−3.8≦f _(G3) /f≦−3  (4)

where

f_(G3) denotes a focal length of the third lens group, and

f denotes the focal length of the entire system of the immersionmicroscope objective.

When the conditional expression (4) is satisfied, the refractive powerof the third lens group becomes appropriately large. This makes itpossible to properly secure the negative Petzval's sum in the third lensgroup, it is possible to enhance flatness of a field.

When exceeding the upper limit of the conditional expression (4), therefractive power of the third lens group will become excessively large.Here, the third lens group has been configured to include theobject-side lens group and the image-side lens group, and in theobject-side lens group, the surface nearest to the image side is theconcave surface facing the image side, and in the image-side lens group,the surface nearest to the object side is the concave surface facing theobject side. In this case, if the refractive power of the third lensgroup becomes excessively large, the radius of curvature of the concavesurface in the object-side lens group and the radius of curvature of theconcave surface in the image-side lens group will both becomeexcessively small. As a result, a large coma will occur.

When falling below the lower limit of the conditional expression (4), itwill become difficult to secure a sufficient negative Petzval's sum inthe third lens group. Therefore, a large curvature of field will occur.As a result, flatness of a field will deteriorate.

Further, in the immersion microscope objective according to the presentembodiment, it is preferable that the second lens group includes atleast an object-side lens component, the object-side lens component isdisposed nearest to the object side and moves in an optical axisdirection, the lens component is a single lens or a cemented lens, andthe following conditional expression (5) is satisfied:

20≦f _(G2o) /f≦50  (5)

where

f_(G2o) denotes a focal length of the object-side lens component, and

f denotes the focal length of the entire system of the immersionmicroscope objective.

Any changes in thickness of the cover glass, type of the immersionliquid, temperature of the specimen or the immersion liquid, orobservation position will cause fluctuation in spherical aberration. Insuch a case, the lens group can be moved in the optical axis directionto correct the spherical aberration. To move the lens group, acorrection collar may be rotated.

Thus, in the objective according to the present embodiment, the secondlens group is configured to be movable. Here, the second lens groupincludes at least the object-side lens component, and the object-sidelens component is disposed nearest to the object side.

As explained above, while the divergent light beam is converted to aconvergent light beam in the first lens group, the divergent light beamis bent gradually. Therefore, the convergent light beam exiting thefirst lens group enters the second lens group with a moderate angle, inthe state where the light-ray height is high. Thus, moving theobject-side lens component in the optical axis direction makes itpossible to newly produce spherical aberration, while suppressing thefluctuation in aberration other than the spherical aberration.

At this time, when the object-side lens component is moved in anappropriate direction, the spherical aberration can be newly produced ina direction opposite to that of the spherical aberration caused by theabove-described changes. Accordingly, the spherical aberration newlyproduced in an appropriate amount can correct the spherical aberrationcaused by the above-described changes.

When the conditional expression (5) is satisfied, the sphericalaberration caused by the above-described changes can be corrected.

When exceeding the upper limit of the conditional expression (5), therefractive power of the object-side lens component will becomeexcessively small. In this case, the amount of movement of theobject-side lens group will increase, but it is difficult to secure asufficient space for the movement. It is thus difficult to adequatelycorrect the spherical aberration.

When falling below the lower limit of the conditional expression (5),the refractive power of the object-side lens component will becomeexcessively large. In this case, when the object-side lens component ismoved, fluctuation in aberration other than the spherical aberration,for example in chromatic aberration, will become large. As a result theoptical performance of the objective will deteriorate.

Further, in the immersion microscope objective according to the presentembodiment, it is preferable that the first lens group includes acemented lens made up of three lenses.

With this configuration, it is possible to favorably correct thelongitudinal chromatic aberration, while maintaining an appropriatepositive refractive power.

A microscope according to the present embodiment includes: a lightsource; an illumination optical system; a main-body section; anobservation optical system; and a microscope objective, wherein theimmersion microscope objective described above is used for themicroscope objective.

The microscope according to the present embodiment includes theimmersion microscope objective which has a large numerical aperture,high magnification, and high flatness of a field, and in which variousaberrations have been corrected sufficiently. Accordingly, it ispossible to observe a sample and acquire an image with high resolvingpower.

It should be noted that each of the conditional expressions may be usedindependently, or may be used freely in combination with any otherconditional expressions. In either case, the effects of the presentinvention are achieved. Further, the upper limit or the lower limit ofany conditional expression may be changed independently. The resultantconditional expression will achieve the effects of the present inventionsimilarly.

Examples of the immersion microscope objective according to the presentinvention will be described in detail below by referring to theaccompanying drawings. It should be noted that the present invention isnot limited to the following examples.

Examples 1 to 3 of the immersion microscope objective according to thepresent invention will be described below. FIGS. 1 to 3 arecross-sectional views along the optical axes, showing the opticalarrangements of the immersion microscope objectives according to theexamples 1 to 3, respectively. In the cross-sectional views, referencenumerals L1 to L17 denote lenses. FIG. 7 is a cross-sectional view of atube lens.

The immersion microscope objectives of the examples 1 to 3 areinfinity-corrected microscope objectives. In an infinity-correctedmicroscope objective, light rays exiting the microscope objective arecollimated, so an image is not formed in itself. Therefore, the parallellight beam is made to converge by a tube lens as shown in FIG. 7, forexample. An image of a sample plane is formed at the position where theparallel light beam converges. In the above description, the image sidemeans the side where the tube lens is disposed.

An objective according to the example 1 will now be described. As shownin FIG. 1, the objective of the example 1 includes, in order from anobject side, a first lens group G1, a second lens group G2, and a thirdlens group G3.

The first lens group G1 has a positive refractive power. The first lensgroup G1 includes, in order from the object side, a planoconvex positivelens L1, a positive meniscus lens L2 having a convex surface facing animage side, a positive meniscus lens L3 having a convex surface facingthe image side, a planoconvex positive lens L4, a biconvex positive lensL5, a negative meniscus lens L6 having a convex surface facing the imageside, and a positive meniscus lens L7 having a convex surface facing theimage side. Here, the planoconvex positive lens L1 and the positivemeniscus lens L2 are cemented together. Further, the biconvex positivelens L5, the negative meniscus lens L6, and the positive meniscus lensL7 are cemented together. It should be noted that the negative meniscuslens L6 and the positive meniscus lens L7 having the convex surfacefacing the image side may be replaced with a planoconcave negative lenshaving a concave surface facing the object side and a planoconvexpositive lens having a convex surface facing the image side,respectively.

The second lens group G2 has a positive refractive power. The secondlens group G2 includes, in order from the object side, a negativemeniscus lens L8 having a convex surface facing the object side, abiconvex positive lens L9, a negative meniscus lens L10 having a convexsurface facing the object side, a biconvex positive lens L11, and anegative meniscus lens L12 having a convex surface facing the imageside. Here, the negative meniscus lens L8 and the biconvex positive lensL9 are cemented together. Further, the negative meniscus lens L10, thebiconvex positive lens L11, and the negative meniscus lens L12 arecemented together.

The third lens group G3 has a negative refractive power. The third lensgroup G3 includes, in order from the object side, a biconvex positivelens L13, a biconcave negative lens L14, a biconcave negative lens L15,a negative meniscus lens L16 having a convex surface facing the imageside, and a positive meniscus lens L17 having a convex surface facingthe image side. Here, the biconvex positive lens L13 and the biconcavenegative lens L14 are cemented together. Further, the negative meniscuslens L16 and the positive meniscus lens L17 are cemented together.

In the first lens group G1 and the third lens group G3, their positionsare fixed. In the second lens group G2, the cemented lens of thenegative meniscus lens L8 and the biconvex positive lens L9 moves alongthe optical axis with respect to the other lenses.

Next, an objective according to the example 2 will be described. Asshown in FIG. 2, the objective of the example 2 includes, in order froman object side, a first lens group G1, a second lens group G2, and athird lens group G3.

The first lens group G1 has a positive refractive power. The first lensgroup G1 includes, in order from the object side, a planoconvex positivelens L1, a positive meniscus lens L2 having a convex surface facing animage side, a positive meniscus lens L3 having a convex surface facingthe image side, a positive meniscus lens L4 having a convex surfacefacing the image side, a biconvex positive lens L5, a biconcave negativelens L6, and a biconvex positive lens L7. Here, the planoconvex positivelens L1 and the positive meniscus lens L2 are cemented together.Further, the biconvex positive lens L5, the biconcave negative lens L6,and the biconvex positive lens L7 are cemented together.

The second lens group G2 has a positive refractive power. The secondlens group G2 includes, in order from the object side, a negativemeniscus lens L8 having a convex surface facing the object side, abiconvex positive lens L9, a negative meniscus lens L10 having a convexsurface facing the object side, a biconvex positive lens L11, and anegative meniscus lens L12 having a convex surface facing the imageside. Here, the negative meniscus lens L8 and the biconvex positive lensL9 are cemented together. Further, the negative meniscus lens L10, thebiconvex positive lens L11, and the negative meniscus lens L12 arecemented together.

The third lens group G3 has a negative refractive power. The third lensgroup G3 includes, in order from the object side, a biconvex positivelens L13, a biconcave negative lens L14, a biconcave negative lens L15,a biconcave negative lens L16, and a biconvex positive lens L17. Here,the biconvex positive lens L13 and the biconcave negative lens L14 arecemented together. Further, the biconcave negative lens L16 and thebiconvex positive lens L17 are cemented together.

In the first lens group G1 and the third lens group G3, their positionsare fixed. In the second lens group G2, the cemented lens of thenegative meniscus lens L8 and the biconvex positive lens L9 moves alongthe optical axis with respect to the other lenses.

Next, an objective according to the example 3 will be described. Asshown in FIG. 3, the objective of the example 3 includes, in order froman object side, a first lens group G1, a second lens group G2, and athird lens group G3.

The first lens group G1 has a positive refractive power. The first lensgroup G1 includes, in order from the object side, a planoconvex positivelens L1, a positive meniscus lens L2 having a convex surface facing animage side, a positive meniscus lens L3 having a convex surface facingthe image side, a positive meniscus lens L4 having a convex surfacefacing the image side, a biconvex positive lens L5, a biconcave negativelens L6, and a biconvex positive lens L7. Here, the planoconvex positivelens L1 and the positive meniscus lens L2 are cemented together.Further, the biconvex positive lens L5, the biconcave negative lens L6,and the biconvex positive lens L7 are cemented together.

The second lens group G2 has a positive refractive power. The secondlens group G2 includes, in order from the object side, a negativemeniscus lens L8 having a convex surface facing the object side, abiconvex positive lens L9, a negative meniscus lens L10 having a convexsurface facing the object side, a biconvex positive lens L11, and anegative meniscus lens L12 having a convex surface facing the imageside. Here, the negative meniscus lens L8 and the biconvex positive lensL9 are cemented together. Further, the negative meniscus lens L10, thebiconvex positive lens L11, and the negative meniscus lens L12 arecemented together.

The third lens group G3 has a negative refractive power. The third lensgroup G3 includes, in order from the object side, a biconvex positivelens L13, a biconcave negative lens L14, a biconcave negative lens L15,a negative meniscus lens L16 having a convex surface facing the imageside, and a positive meniscus lens L17 having a convex surface facingthe image side. Here, the biconvex positive lens L13 and the biconcavenegative lens L14 are cemented together. Further, the negative meniscuslens L16 and the positive meniscus lens L17 are cemented together.

In the first lens group G1 and the third lens group G3, their positionsare fixed. In the second lens group G2, the cemented lens of thenegative meniscus lens L8 and the biconvex positive lens L9 moves alongthe optical axis with respect to the other lenses.

Next, numerical data of optical members forming the objective of theabovementioned examples is given below. In the numerical data for eachexample, r denotes a radius of curvature of each lens surface (however,r1 and r2 are virtual surfaces), d denotes a thickness of each lens oran air space (however, d1 denotes a thickness of a cover glass, and d2denotes a thickness of an immersion liquid layer), nd denotes therefractive index of each lens for a d-line, νd denotes Abbe number foreach lens, β denotes magnification, NA denotes the numerical aperture, fdenotes a focal length of the overall objective, WD denotes a workingdistance, and FN denotes a field number. The magnification β is amagnification when combined with a tube lens that will be describedlater (focal length 180 mm). Further, WD denotes the distance when thecover glass has a thickness of 0.17 mm. The field number is 22 mm.

Numerical data in each example show data in the state where there is acover glass between a sample and the objective. In this state, an imageof the sample is formed via the cover glass and the immersion liquid. Inthis case, the virtual surface r1 indicates a boundary between thesample plane and the cover glass, and the virtual surface r2 indicates aboundary between the cover glass and the immersion liquid. As theimmersion liquid and the biological specimen have their refractiveindices close to each other, in the state where the distance between thecover glass and the objective is smaller than the value of d2, thefluorescent light caused by the light ray from the sample plane, thathad reached the interior of the specimen from the virtual surface r1,enters the objective with few aberrations. It is thus evident that theinterior of the sample can be observed. The radius of curvature r, thesurface separation d, the focal length f, and the working distance WDare all shown in millimeters (mm).

Example 1

B = −100, NA = 1.35, f = 1.8, WD = 0.217, FN = 22 Surface data Surfaceno. r d nd νd 1 ∞ d1  1.52100 56.02 2 ∞ d2  1.40409 51.90 3 ∞ 1.00381.45852 67.83 4 −3.8000 2.9493 1.88300 40.76 5 −3.4688 0.1500 6 −6.68551.7804 1.75500 52.32 7 −5.7540 0.1510 8 ∞ 2.5350 1.59522 67.74 9−12.3287 0.1672 10 27.4440 6.1576 1.43875 94.93 11 −7.9036 1.15001.63775 42.41 12 −2553.4402 3.9799 1.43875 94.93 13 −10.9049 d13 1433.7194 1.1000 1.63775 42.41 15 7.8248 5.5131 1.43875 94.93 16 −19.3175d16 17 9.6846 1.0000 1.63775 42.41 18 5.9012 4.9087 1.43875 94.93 19−9.4714 0.8000 1.61336 44.49 20 −24.9286 0.4775 21 5.1797 2.5301 1.4970081.54 22 −21.3115 1.5338 1.63775 42.41 23 2.3963 1.6836 24 −3.94610.7000 1.77250 49.60 25 8.8980 3.7400 26 −5.9356 1.1550 1.61336 44.49 27−60.4766 2.3410 1.73800 32.26 28 −5.7630 Various data d1 0.13 0.17 0.19d2 0.2446 0.2170 0.2036 d13 0.4373 0.9473 1.2273 d16 1.0288 0.51880.2388

Example 2

B = −100, NA = 1.35, f = 1.8, WD = 0.217, FN = 22 Surface data Surfaceno. r d nd νd 1 ∞ d1  1.52100 56.02 2 ∞ d2  1.40409 51.90 3 ∞ 0.71011.45852 67.83 4 −3.3200 2.9351 1.88300 40.76 5 −3.2933 0.1500 6 −5.55381.7838 1.74100 52.64 7 −5.0869 0.1500 8 −146.1257 2.6771 1.59522 67.74 9−10.7389 0.1500 10 29.5466 6.1582 1.43875 94.93 11 −7.4591 1.10001.63775 42.41 12 175.8765 4.4572 1.43875 94.93 13 −10.4332 d13 1419.2142 1.0000 1.63775 42.41 15 7.4207 5.4946 1.43875 94.93 16 −25.8615d16 17 9.5298 1.0000 1.63775 42.41 18 5.7485 5.1463 1.43875 94.93 19−8.4216 0.8000 1.51633 64.14 20 −61.9312 0.6936 21 6.4042 2.4908 1.4970081.54 22 −9.2067 1.4271 1.63775 42.41 23 2.5854 1.5639 24 −3.9518 0.63911.61340 44.27 25 8.2481 2.8414 26 −5.2486 1.3103 1.61336 44.49 27146.0111 2.9850 1.73800 32.26 28 −5.9005 Various data d1 0.13 0.17 0.19d2 0.2407 0.2170 0.2056 d13 0.3410 0.8110 1.0610 d16 0.9678 0.49780.2478

Example 3

B = −100, NA = 1.35, f = 1.8, WD = 0.203, FN = 22 Surface data Surfaceno. r d nd νd 1 ∞ d1  1.52100 56.02 2 ∞ d2  1.40409 51.90 3 ∞ 1.42601.45852 67.83 4 −5.5000 2.8477 1.88300 40.76 5 −3.8145 0.1500 6 −10.36821.7892 1.75500 52.32 7 −7.3992 0.1500 8 −59.0521 2.1781 1.59522 67.74 9−12.8963 0.1700 10 15.3806 6.3765 1.43875 94.93 11 −9.7346 1.00001.63775 42.41 12 33.0053 4.4661 1.43875 94.93 13 −12.7945 d13 14 27.83691.0010 1.63775 42.41 15 7.6694 5.7350 1.43875 94.93 16 −22.6935 d16 179.0865 1.0000 1.63775 42.41 18 5.9431 4.9670 1.43875 94.93 19 −9.41710.8000 1.61336 44.49 20 −24.6607 0.1064 21 4.6890 2.5288 1.49700 81.5422 −15.3963 1.6444 1.63775 42.41 23 2.0303 1.9348 24 −3.1219 0.70001.77250 49.60 25 15.1148 4.0078 26 −6.6909 0.7233 1.61336 44.49 27−11.9643 1.8568 1.73800 32.26 28 −5.1821 Various data d1 0.13 0.17 0.19d2 0.2321 0.2030 0.1884 d13 0.4197 0.9297 1.1797 d16 1.0495 0.53950.2895 Tube lens Surface data Surface no. r d nd νd 1 68.7541 7.73211.48749 70.23 2 −37.5679 3.4742 1.80610 40.92 3 −102.8477 0.6973 484.3099 6.0238 1.83400 37.16 5 −50.7100 3.0298 1.64450 40.82 6 40.6619focal length 180

FIGS. 4A, 4B, 4C, and 4D to FIGS. 6A, 6B, 6C, and 6D are aberrationdiagrams of the objectives according to the examples 1 to 3. Theaberration diagrams of each example show the aberrations in the casewhere the distance between the immersion microscope objective and thetube lens is 120 mm. FIGS. 4A, 5A, and 6A each show spherical aberration(SA), FIGS. 4B, 5B, and 6B each show astigmatism (AS), FIGS. 4C, 5C, and6C each show coma (DZY), and FIGS. 4D, 5D, and 6D each show chromaticaberration of magnification (CC). Further, “IMH” shows an image height.

Next, the values of conditional expressions (1) to (5) in each exampleare shown below.

Conditional expressions Example1 Example2 Example3 (1)(r_(G12)/f) ×(NA_(ob)/nd_(imm))² −1.95 −1.71 −2.81 (2)nd_(G1i) − nd_(G1o) 0.42 0.420.42 (3)f_(G1p)/f 2.77 2.74 2.74 (4)f_(G3)/f 33.13 24.06 33.48(5)f_(G2o)/f −3.5 −3.51 −3.43

FIG. 8 is a diagram showing the microscope according to the presentembodiment. In FIG. 8, an example of an external structure of a laserscanning microscope is shown as an example of the microscope. As shownin FIG. 8, a microscope 10 includes a main body section 1, an objective2, a revolver 3, an objective raising and lowering mechanism 4, a stage5, an epi-illumination unit 6, an observation lens barrel 7, and ascanner 8. Moreover, an image processing apparatus 20 is connected tothe microscope 10, and an image display apparatus 21 is connected to theimage processing apparatus 20. In the microscope according to thepresent embodiment, the immersion microscope objective according to thepresent embodiment is used for the objective 2.

The stage 5 is provided to the main body section 1. A sample 9 is to beplaced on the stage 5. Moreover, the epi-illumination unit 6 is providedat an upper side of the main body section 1. Epi-illumination visiblelight is irradiated to the sample 9 by the epi-illumination unit 6.Light from the sample 9 travels through the objective 2, and reaches theobservation lens barrel 7. A user is able to observe the sample 9through the observation lens barrel 7 in visible light.

Moreover, a laser source (not shown in the diagram) and the scanner 8are provided at a rear side (right side of a paper surface) of the mainbody section 1. The laser source and the scanner 8 are connected by afiber (not shown in the diagram). The scanner 8 includes a galvanometerscanner and a photo detection element, which are disposed at an interiorof the scanner 8. The laser source is a laser which generates aninfrared light that can operate two-photon excitation. Light from thelaser source, after travelling through the scanner 8 is incident on theobjective 2. The objective 2 is positioned at a lower side of the stage5. Therefore, the sample 9 is illuminated from a lower side as well.

Light (reflected light or fluorescent light) from the sample 9, upontravelling through the objective 2, passes through the scanner 8, and isdetected by the photo detection element. In the two-photon excitation,since fluorescent light generates only focal point, a confocalobservation is possible. In the confocal observation, it is possible toobtain a cross-sectional image of the sample 9.

The objective raising and lowering mechanism 4 is connected to therevolver 3. The objective raising and lowering mechanism 4 is capable ofmoving the objective 2 (the revolver 3) along an optical axialdirection. In a case in which, a plurality of cross-sectional imagesalong the optical axial direction of the sample 9 are to be obtained,the objective 2 is to be moved by the objective raising and loweringmechanism 4.

A signal obtained by the photo detection element is transmitted to theimage processing apparatus 20. An image processing is carried out in theimage processing apparatus 20, and an image of the sample 9 is displayedon the image display apparatus 21.

In the example described above, the immersion microscope objectiveaccording to the present embodiment has been used for the two-photonexcitation observation. However, it is also possible to use theimmersion microscope objective according to the present embodiment for atotal internal reflection fluorescence observation. In such case, adiameter of a bundle of rays from the laser source is to be kept smallerthan an effective aperture of the immersion microscope objective.Moreover, an arrangement is to be made such that, the bundle of raysfrom the laser source is made to be incident on the immersion microscopeobjective such that it does not include an optical axis of the immersionmicroscope objective.

Further, the immersion microscope objective of the present embodimentmay be used for a conventional microscope using a xenon lamp or halogenlamp.

It should be noted that in the examples 1 to 3, silicone having therefractive index of 1.40409 for the d-line was used as the immersionliquid. Alternatively, an immersion liquid as a mixture of glycerin andwater, having a similar refractive index, may be used. Furthermore,various modifications can be made to the present invention withoutdeparting from the scope thereof.

According to the present invention, it is possible to provide animmersion microscope objective which has a large numerical aperture,high magnification, and high flatness of a field, and in which variousaberrations have been corrected sufficiently, and also provide amicroscope using the immersion microscope objective.

As described above, the present invention is suitably applicable to animmersion microscope objective which has a large numerical aperture,high magnification, and high flatness of a field, and in which variousaberrations have been corrected sufficiently, and to a microscope usingthe immersion microscope objective.

What is claimed is:
 1. An immersion microscope objective comprising, inorder from an object side: a first lens group having a positiverefractive power; a second lens group having a positive refractivepower; and a third lens group having a negative refractive power;wherein the first lens group includes a first lens surface and a secondlens surface, the first lens surface is positioned nearest to the objectside, and the second lens surface is positioned on an image side of thefirst lens surface and nearest to the first lens surface, and thefollowing conditional expression (1) is satisfied:−3≦(r _(G12) /f)×(NA _(ob) /nd _(imm))²≦1.7  (1) where r_(G12) denotes aradius of curvature at the second lens surface, f denotes a focal lengthof an entire system of the immersion microscope objective, NA_(ob)denotes an object-side numerical aperture of the immersion microscopeobjective, and nd_(imm) denotes a refractive index of an immersionliquid for a d-line.
 2. The immersion microscope objective according toclaim 1, wherein the first lens group converts a divergent light beam toa convergent light beam, the third lens group includes an object-sidelens component and an image-side lens component, the object-side lenscomponent is disposed nearest to the object side, and the image-sidelens component is disposed closer to the image side than the object-sidelens component, the object-side lens component has a meniscus shape witha concave surface facing the image side, the image-side lens componenthas a meniscus shape with a concave surface facing the object side, andthe lens component is a single lens or a cemented lens.
 3. The immersionmicroscope objective according to claim 1, wherein the first lens groupincludes a first cemented lens disposed nearest to the object side, thefirst cemented lens includes an object-side lens and an image-side lens,and the following conditional expression (2) is satisfied:0.3≦nd _(G1i) −nd _(G1o)≦0.5  (2) where nd_(G1i) denotes a refractiveindex of the image-side lens for the d-line, and nd_(G1o) denotes arefractive index of the object-side lens for the d-line.
 4. Theimmersion microscope objective according to claim 1, wherein the firstlens group includes, in order from the object side, a cemented lens anda single lens, the cemented lens and the single lens each have apositive refractive power, and the following conditional expression (3)is satisfied:2.2≦f _(G1p) /f≦3.5  (3) where f_(G1p) denotes a composite focal lengthof the cemented lens and the single lens, and f denotes the focal lengthof the entire system of the immersion microscope objective.
 5. Theimmersion microscope objective according to claim 1, wherein the thirdlens group satisfies the following conditional expression (4):−3.8≦f _(G3) /f≦−3  (4) where f_(G3) denotes a focal length of the thirdlens group, and f denotes the focal length of the entire system of theimmersion microscope objective.
 6. The immersion microscope objectiveaccording to claim 1, wherein the second lens group includes at least anobject-side lens component, the object-side lens component is disposednearest to the object side and moves in an optical axis direction, thelens component is a single lens or a cemented lens, and the followingconditional expression (5) is satisfied:20≦f _(G2o) /f≦50  (5) where f_(G2o) denotes a focal length of theobject-side lens component, and f denotes the focal length of the entiresystem of the immersion microscope objective.
 7. The immersionmicroscope objective according to claim 1, wherein the first lens groupincludes a cemented lens made up of three lenses.
 8. A microscopecomprising: a light source; an illumination optical system; a main-bodysection; an observation optical system; and a microscope objective,wherein the immersion microscope objective recited in claim 1 is usedfor the microscope objective.